For major deal windows (Black Friday, Cyber Monday, and other tent-pole events), CPCs spike and non-deal listings convert poorly. The decision is binary and made per client: if a seller isn't running an actual deal for the event, ads are turned off entirely on those specific days to protect spend, rather than merely reduced — the reasoning being that with no deal, there's no realistic chance of converting efficiently against inflated, deal-driven competition. Clients who are participating go the other way: advertise aggressively and budget for the elevated CPCs.
For sellers who do participate with seasonal/gift products, gift-related keywords get notably more expensive in Q4; Brand Analytics top search terms help prioritize the most reasonable keywords rather than bidding on all of them ('don't boil the ocean'). Related: Holiday/Event Pricing Strategy, Amazon Search Query Performance (SQP) Report.